An investigation of the development of phonology in Spanish-and English-learning infants during the first 30 months of life is proposed. This primarily longitudinal study will integrate the results of speech perception and speech production research into a single framework. The primary methodologies for study of speech production will be specially modified transcription and categorization systems, as well as acoustic analysis. Methodologies for perception studies will be the VRISD (Visually Reinforced Infant Speech Discrimination) and Shell Game paradigms. The proposed study will provide a body of data which will (1) contribute to the scientific study of phonological learning from a cross-linguistic perspective; (2) provide needed clinical information on normal development for both Spanish- and English-learning infants.